Fluid spray guns are generally known and are commonly used to spray a wide variety of fluids on any number of different types of articles. Spray guns can be used, for example, to spray fluids such as paint, lacquer, cleansers, sealants and so forth. Fluid spray guns may be hand operated or automatic depending on the specific application system requirements.
Fluid spray technology includes a number of spraying modes or spraying processes for applying a fluid to an object. A fundamental characteristic of all spray processes is that the fluid is atomized before it is applied to the object being sprayed. The spray processes differ in the manner by which the fluid is atomized, with the goal being a finely atomized spray that is released from the spray gun in a well defined spray pattern. The spray pattern can be shaped by the selected atomization process as well as by the design of the spray nozzle used with the spray gun. Thus, different spray technologies not only use different atomization processes but also may use different nozzle designs.
A familiar spray process is air spraying which utilizes pressurized air to atomize the fluid at the region of the spray nozzle outlet. Air spray guns thus tend to be operated at lower fluid pressures such that in the absence of an atomizing air supply the fluid simply runs out the nozzle as a small stream. The atomizing air is usually on the order of 10 to 100 psi. Therefore, the spray gun must be able to withstand such air pressures.
In some cases it is desirable or required to operate air spray guns at a reduced air pressure. Using lower atomizing air pressure may in some cases reduce fluid bounce back from the object being sprayed and thus increase transfer efficiency. Such spraying systems are generally referred to as using a high volume low pressure (“HVLP” hereinafter) spray process. In a typical HVLP process, the air pressure at the nozzle is kept to less than 10 psi but the spray nozzle is designed to increase the volume of air directed at the fluid spray. Thus, HVLP is a variation of air spray technology but utilizes a different spray nozzle design. Spray guns for HVLP operation also require a mechanism by which the air pressure at the nozzle can be tested for compliance with the under 10 psi requirement.
In both air spray and HVLP spray processes, the atomization air may not fully atomize the fluid or may produce an undesired spray pattern. Air spray guns therefore also utilize horn air. Horn air is a second source of pressurized air that is applied to an outer region of the atomized fluid spray pattern to shape the spray pattern and also to improve atomization of the fluid in the outer regions of the spray pattern.
Another fluid spray process is airless spraying. As suggested by the name, an airless spray process does not use high pressure air for primary atomization of the fluid. Rather, the fluid is supplied under high pressure to a small orifice in the spray nozzle. The kinetic energy applied to the liquid as it passes through the orifice breaks apart the fluid stream into a finely atomized spray, much like a garden hose nozzle produces a spray of water. In airless spray apparatus the fluid may be pressurized up to 1500 psi or higher although many airless spray guns operate at lower fluid pressures, for example 900-1000 psi. An airless spray nozzle is therefore different from an air spray nozzle in order to effect a desired spray pattern and adequate atomization.
Airless spray guns sometimes produce an effect generally known as tailing in which the fluid near the outer region of the spray pattern is not atomized to the same extent as in the center region of the pattern. This effect can reduce the overall quality of the finished product. In order to eliminate tailing and to further improve the atomization process, an air assisted airless (“AAA” hereinafter) spray process may be used. In such a process, although primary atomization occurs due to high pressure fluid passing through the nozzle orifice, atomization air may also be supplied and directed at the spray pattern in the region of the nozzle outlet.
Because each of the above described spraying processes utilizes different atomization and nozzle designs, it is not surprising that known spray guns usually only operate with a single spray process. Thus, there are airless spray guns, air spray guns, AAA guns and HVLP guns. For example, an airless spray gun does not have the hardware needed for air spray operation. An air spray gun typically will not operate as an airless gun. An air assisted airless gun will have air supplied to it, but typically will not operate satisfactorily as a true air spray gun.
Because these guns all use different spray technologies and nozzle designs, a spray gun manufacturer must keep a significant inventory of parts to build each gun type. Spray gun users may also need to keep a variety of spare parts to repair such guns.
Another spray technology is corona discharge electrostatic spraying in which an electrostatic charge is applied to the fluid as it is dispersed out the nozzle. The electrostatic charge helps to atomize the fluid, but more importantly is used to improve the transfer efficiency by utilizing the electrostatic attraction between the charged fluid and the object being sprayed. Electrostatic guns thus can utilize air spray technology such as air assisted and airless air assisted and HVLP. Accordingly, known electrostatic gun designs include the same problems of numerous parts, different gun designs for each technology and so forth as described hereinabove.
It is desired therefore to provide a new spray gun apparatus that can utilize a number of different fluid spray technologies using basic shared components that can be easily configured for a specific application.